How to finish over nail plates in plaster ceiling?

Hello! First time, thanks for having me.

I'm in the process of replacing the knob and tube in my 100 year-old house with with romex wire. Almost all of the walls and ceilings are plaster and lathe. For the ceiling fixtures I had to run wire perpendicular to the joists and often cut about a 3 x 5 inch hole in the plaster (not the lathe) perpendicular to and centered on the joists. I removed the plaster in the exposed key (between the lathe) and ran the new romex wire in that space when it crossed the joist. I plan on covering the wires with nail plates to prevent someone (most likely myself in a few years) from screwing into wires.



My question is regarding the best way to repair and finish the approximately 1/4" deep of missing plaster. If it weren't for the nail plates I'd just dust the lathe off and apply a few coats of joint compound. Any suggestions on how to make sure the joint compound sticks to the nail plate and lathe? I've found several ideas online: PVA primer, drywall mesh tape, etc but none specific to metal on ceilings. Or perhaps there's a better approach all together? This is definitely the first time I've repaired plaster ceilings and i'm adding metal substrate to the scenario to complicate matters.

Thanks very much!!

 

Install the mail guards. Paint them with bonding agent. While you are at it get th lath, not lathe, too. Spread on a coat of setting joint compound but don't make it flush yet. Get some wide joint tape like the self adhesive stuff only six inches wide. Cut it to fit the hole. Put it in and give it another coat of mud. Maybe yet one more coat will finish the job.
One more thing. When you are painting bonding agent, get the edges of the hole too

 

Kind of a big hole for one wire. I usually only make a notch a little over an inch wide. Just wide enough for a narrow nail plate.

You're going to need to notch the stud you crossed so that the nail plate will sit flush with the lath strips.

 

Thanks guys!
I'll pick up some Plaster Weld, EZ Sand 45, and wide self-adhesive mesh tape today. Unless you think other products would be better? Really appreciate your input.

 

Since I don't have any plaster skills I always use drywall products to repair plaster. If it was me, I'd install a piece of drywall just shy of even and then use durabond [easy sand also works well] over it. Looks like you might need 1/4" drywall .... BUT you can go wrong following tightcoat's advice!

 

I am thinking there. Will still be some recess of the nail plate such that here will not be a hump in he repair. If that will not be th case en a notch as PJ suggests will be good insurance. I would forego the new drywall just to save a step and in order to keep the repair flat. You can even embed th mesh in the first coat of mud. I just think it will do mOre good in a second coat. We're the wire recessed enough that the nail plate was close to flush with the path I would slap a piece of light gauge metal lath over it and do it with plaster. I just think joint compound is more amateur friendly.

 

that was supposed to read 'you can't go wrong following tightcoat's advice'